NBC News is expanding on a report from CNN this morning that congressional investigators are exploring a potential previously undisclosed meeting last year between then-Sen. Jeff Sessions and Russian Ambassador Sergey Kislyak. NBC is reporting that the FBI and lawmakers are looking into whether that potential meeting also included Donald Trump and his son-in-law Jared Kushner.

Five current and former U.S. officials said they are aware of classified intelligence suggesting there was some sort of private encounter between Trump and his aides and the Russian envoy, despite a heated denial from Sessions, who has already come under fire for failing to disclose two separate contacts with Kislyak. Kushner also denied through a spokesman that he met privately with Kislyak that day.

The officials acknowledged to NBC News that the evidence does not amount to proof, and they have declined to provide details about it. [...]

CNN reported Wednesday about the investigative interest in the Mayflower event, which took place on April 27, 2016. NBC News has been discussing the matter with knowledgeable sources for weeks, seeking more clarity about why Congressional investigators believe there may have been a private meeting.

NBC also reports that the Mayflower event was sponsored by a pro-Russian think thank.

On MSNBC Wednesday night, Sen. Al Franken (D-MN) said that he and Sen. Patrick Leahy (D-VT) had knowledge of the Mayflower event and had "reason to believe" there might be more to the interactions between Sessions and Kislyak at the event than had been previously indicated.

"It had been characterized one way, but we had some reason to believe that wasn't the case," Franken said about the event. "It had been described in a way that he could say, 'I don't remember that.'"

Franken added, "If this the true, that would be extremely disturbing."

You can watch the Franken clip below.